netdev - Re: [RFC PATCH v2 net-next 0/4] txhash: Make hash rethink configurable

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Message-Id: <69C55C6B-02FC-429D-BD25-AA0D78EADCFF@yandex-team.ru>
Date:   Tue, 23 Nov 2021 16:20:55 +0300
From:   Akhmat Karakotov <hmukos@...dex-team.ru>
To:     hmukos@...dex-team.ru
Cc:     Eric Dumazet <eric.dumazet@...il.com>,
        Alexander Azimov <mitradir@...dex-team.ru>,
        netdev@...r.kernel.org, tom@...bertland.com, zeil@...dex-team.ru
Subject: Re: [RFC PATCH v2 net-next 0/4] txhash: Make hash rethink
 configurable

Hi Eric,

I've sent v2 of the patch. I've removed confusing part with sysctl default values
and made other changes according to your comments. I look forward for your
review.

> On Nov 12, 2021, at 21:19, Akhmat Karakotov <hmukos@...dex-team.ru> wrote:
> 
> As it was shown in the report by Alexander Azimov, hash rethink at the
> client-side may lead to connection timeout toward stateful anycast
> services. Tom Herbert created a patchset to address this issue by applying
> hash rethink only after a negative routing event (3RTOs) [1]. This change
> also affects server-side behavior, which we found undesirable. This
> patchset changes defaults in a way to make them safe: hash rethink at the
> client-side is disabled and enabled at the server-side upon each RTO
> event or in case of duplicate acknowledgments.
> 
> This patchset provides two options to change default behaviour. The hash
> rethink may be disabled at the server-side by the new sysctl option.
> Changes in the sysctl option don't affect default behavior at the
> client-side.
> 
> Hash rethink can also be enabled/disabled with socket option or bpf
> syscalls which ovewrite both default and sysctl settings. This socket
> option is available on both client and server-side. This should provide
> mechanics to enable hash rethink inside administrative domain, such as DC,
> where hash rethink at the client-side can be desirable.
> 
> [1] https://lore.kernel.org/netdev/20210809185314.38187-1-tom@herbertland.com/
> 
> v2:
> 	- Changed sysctl default to ENABLED in all patches. Reduced sysctl
> 	  and socket option size to u8. Fixed netns bug reported by kernel
> 	  test robot.
> 
> Akhmat Karakotov (4):
>  txhash: Make rethinking txhash behavior configurable via sysctl
>  txhash: Add socket option to control TX hash rethink behavior
>  bpf: Add SO_TXREHASH setsockopt
>  tcp: change SYN ACK retransmit behaviour to account for rehash
> 
> arch/alpha/include/uapi/asm/socket.h  |  2 ++
> arch/mips/include/uapi/asm/socket.h   |  2 ++
> arch/parisc/include/uapi/asm/socket.h |  2 ++
> arch/sparc/include/uapi/asm/socket.h  |  2 ++
> include/net/netns/core.h              |  1 +
> include/net/sock.h                    | 28 ++++++++++++++-------------
> include/uapi/asm-generic/socket.h     |  2 ++
> include/uapi/linux/socket.h           |  4 ++++
> net/core/filter.c                     | 10 ++++++++++
> net/core/net_namespace.c              |  2 ++
> net/core/sock.c                       | 13 +++++++++++++
> net/core/sysctl_net_core.c            | 15 ++++++++++++--
> net/ipv4/inet_connection_sock.c       |  3 +++
> net/ipv4/tcp_output.c                 |  3 ++-
> 14 files changed, 73 insertions(+), 16 deletions(-)
> 
> -- 
> 2.17.1
>